Action Points

Note that this proof-of-concept study identified upregulated genes in patients with granulomatosis with polyangiitis.

Be aware that, while controls were used, larger studies will be needed to determine which of these genes are actually relevant to GPA.

Whole genome gene expression profiling of the superficial tissue within the nose of patients with granulomatosis with polyangiitis (GPA) showed upregulation of genes involved in the innate immune system, in maintaining integrity of the epithelial barrier, and in extracellular matrix composition, researchers reported online in Arthritis and Rheumatology.

Among the pathways that were upregulated in nasal brushings from patients with GPA were those involved in adhesion and diapedesis -- the movement of leukocytes out of the circulation and toward the site of tissue damage -- of granulocytes and agranulocytes, interleukin-10 signaling, and TREM1 (triggering receptor expressed on myeloid cells 1) signaling.

The top differentially expressed nasal gene was TREM1, with a greater than threefold change (fold change 3.06, P=4.8 E-04) compared with controls, according to Peter C. Grayson, MD, head of the Vasculitis Translational Research Program, National Institute of Arthritis and Musculoskeletal and Skin Diseases, NIH, in Bethesda, Md., and colleagues.

"TREM1 is a signaling receptor on neutrophils and monocytes that amplifies pro-inflammatory cytokine production, degranulation, and phagocytosis in response to bacterial stimuli," all important functions of the innate immune system.

"Increased serum levels of soluble TREM1 have been associated with disease activity in ANCA [antineutrophil cytoplasmic autoantibody]-associated vasculitis. TREM1 may serve as an important mediator between the nasal microbiome and disease pathogenesis in GPA," the researchers explained.

Nasal involvement is common in GPA, and is characterized by crusting, bleeding, and eventual destruction of cartilage and bone. In many patients it's the first manifestation of this systemic vasculitis.

"Patients with GPA often come to medical attention complaining of nosebleeds and sinus tenderness. These patients are often treated for presumed sinus infections for months and even years until other features of vasculitis begin to appear," Grayson told MedPage Today.

Typical histologic findings of nasal tissue in GPA include small vessel vasculitis, granulomatous inflammation, and necrosis, but diagnostic accuracy of biopsy specimens in these patients is relatively low, at only about 50%.

In addition, the upper airway involvement can persist during treatment even with improvements in other affected systems. Accordingly, more precise means of diagnosing the disease and differentiating active nasal disease from chronic damage are needed.

Most gene expression profiling studies of rheumatologic diseases have been done using blood because it's easily accessible, but Grayson and colleagues hypothesized that it would be more informative to perform the tests on tissue from the site of injury. "We think of the nose as a window into the disease that may provide us with a lot of insight into the causal mechanisms," he said.

They therefore undertook a proof-of-concept study in which they obtained brushings from the right inferior turbinate from 32 patients who met the American College of Rheumatology criteria for GPA.

Among those patients, 10 had active nasal disease, 13 had past nasal involvement, and nine had never developed nasal disease.

A composite control group consisted of 12 healthy volunteers, 15 with biopsy-confirmed sarcoidosis, and eight with active allergic rhinitis, while a second comparator group consisted of 12 patients with eosinophilic granulomatosis with polyangiitis (EGPA), a vasculitis that shares some features with GPA.

RNA was obtained from brushing samples of all participants, and differential gene expression was compared among all subgroups, with adjustments on linear regression analysis for treatment with glucocorticoids and other immunosuppressive medications.

A total of 339 genes showed differential expression in the GPA group and the composite comparator group, including some responsible for structural proteins in the epithelium such as keratin. Other genes that were differentially expressed were those associated with chemotaxis of neutrophils, such as IL-8 and CXCR1, with inflammation, such as IL1, and with toll like receptors such as TLR2.

Differences also were seen between the three GPA subgroups, with only 18 genes in all three being differentially expressed compared with the composite control group. Genes that were upregulated in all three subgroups included those that encode fibronectin 1 (FN1) and desmoglein-3 (DSG3), which are involved in cellular adhesion, while SPARCL1 was downregulated.

Among 48 genes that were upregulated only in patients with past GPA nasal disease were KLK13, which encodes kallikrein-13, and IL36A, which encodes interleukin-36 alpha. This difference in gene expression between active and past disease "may reflect changes in gene expression related to nasal damage," the researchers explained.

An additional group of differentially expressed genes were independent of disease status (active or past), such as SPP1, which encodes the matricullar protein osteopontin involved in granuloma formation in GPA.

Five candidate genes were then chosen for validation using real time PCR, based on the degree of differential expression and established association with GPA, and included TREM1 and SERPINA1, which encodes for alpha-1 antitrypsin.

"Increased SERPINA1 expression in nasal mucosa of patients with GPA raises the possibility of a protease-antiprotease imbalance in the nasal environment that could play a causal role in the development of GPA," Grayson and colleagues wrote.

"The study has given us a really nice list of candidate genes and ideas and pathways to pursue in future experiments," Grayson said.

"The observation that some of the genes we detected were related to the innate immune system suggested that there may be interactions going on between the nasal microbiome and immune cells within the nose. That's a really attractive idea for us to follow," he said in an interview.

They also plan to examine gene expression in deeper nasal tissue biopsy samples.

A limitation of the study was the small number of patients in the GCA subgroups, while a strength was the use of controls with relevant diseases such as rhinitis, sarcoidosis, and EGPA, which increased "the likelihood that identified gene expression signatures were specific to GPA and not generic to nasal inflammation."

The study was supported by NIAMS and the Vasculitis Research Fund at Boston University.

Grayson has received support from a Rheumatology Scientist Development Award from the Research and Education Foundation of the American College of Rheumatology.

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